1. Field of the Invention
The present invention relates to an action mechanism for a keyboard o an electronic piano, which is adapted to have a touch similar to that of an ordinary piano.
2. Description of Prior Art
As illustrated in FIG. 1 which is a side view of a conventional action mechanism for a keyboard of an electronic piano, a key member 1 is supported by a balance rail 6 in such a manner that the key member 1 is allowed to move seesaw with respect to the balance rail 6. The key member 1 is provided with a counter weight 3 at one free end (rear end) thereof so as to apply reaction force to the key member 1 upon depression of the key member 1, whereby the electronic piano is designed to have a touch similar to that of an ordinary piano during playing.
Significant features of a touch of the ordinary piano as natural instruments reside in that:
there occurs a reaction force which acts to fingers of a player upon depression of key members, the reaction force being classified to an impact force when the fingers of player touch the key members and a reaction force generated when a hammer of the action mechanism moves with a delay to the depression movement of the key members;
the reaction force of the hammer described hereinabove varies in response to strength in the depression of key members; and
a static force of key members shows hysteresis characteristic in one stroke including movements in depression and restoring directions.
An example of the reaction force of the hammer of the ordinary piano is shown in FIG. 2 and an example of the hysteresis characteristic is shown in FIG. 3.
In FIG. 2, a horizontal axis plots the movement length (stroke) of the key member upon depression thereof, and a vertical axis plots a dynamic reaction force of the hammer hitting a string, characters f, ff and fff indicating "forte", "fortissimo" and "fortissisimo".
When the depression of key member is commenced, the key member starts lifting a jack to thereby swing a hammer pad, i.e., the hammer. A summit (a point of inflection) which occurs first in each of curves shown in FIG. 2, shows a point where the dynamic reaction force of the hammer shows maximum. When the key member is further depressed, the jack releases the hammer pad at a position predetermined by the function of a regulation button, as a result of which no force actuates the hammer and then the dynamic reaction force starts decreasing from the first occurrence inflection point. In this case, the hammer swings to hit the string, and therefore the hitting causes a second inflection point in the curve of FIG. 2 to occur. Thereafter, the curves show decreasing gradually. FIG. 3 shows that the static depression force applied to the key member in the depression movement is different from that in the restoring movement.
With such an action mechanism for the keyboard of the conventional electronic piano, it may be impossible to realize a touch similar to that of an ordinary piano as natural instruments, that complies with the players' requirement.